1. Technical Field of the Invention
This invention is related to signal processing circuits in general and for cold cathode pressure gauges as a particular example application.
2. State of the Prior Art
Cold cathode gauges are used to measure pressures in ultra-high vacuum (UHV) systems or chambers, i.e., ultra-low pressure ranges. They are accurate and sensitive for pressures ranging from 10−2 torr down to 10−9 torr. A variation of a cold cathode gauge, known in the art as an inverted magnetron, can measure down to 10−12 torr. Therefore, cold cathode gauges are used not only for measuring pressures in such UHV systems or chambers, but signal outputs from cold cathode gauges are useful for myriad process and control applications in which ultra-high vacuums are used.
In typical cold cathode gauges, electrons produced in the discharge of a high voltage travel through the gauge and ionize gas molecules around them. The resulting ions are collected at a negative electrode, and the current depends on the number of ions, which depends on the pressure in the gauge. Consequently, the ion current in a cold cathode gauge is proportional to the pressure in the gauge and can be used as an output signal that is indicative of pressure. For example, for pressures in a range of 10−3 to 10−8 torr the relationship between the ion current and pressure is i=kPn, where i is the ion current, k is a constant related to the particular gas or gases in the system or chamber and other characteristics of the particular cold cathode gauge, P is the pressure, and n is a constant.
The foregoing examples of related art and limitations related therewith are intended to be illustrative, but not exclusive or exhaustive, of the subject matter. Other aspects and limitations of the related art will become apparent to those skilled in the art upon a reading of the specification and a study of the drawings.